userfaultfd: untag user pointers

userfaultfd: untag user pointers

This patch is a part of a series that extends kernel ABI to allow to pass
tagged user pointers (with the top byte set to something else other than
0x00) as syscall arguments.

userfaultfd code use provided user pointers for vma lookups, which can
only by done with untagged pointers.

Untag user pointers in validate_range().

Link: http://lkml.kernel.org/r/cdc59ddd7011012ca2e689bc88c3b65b1ea7e413.1563904656.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <[email protected]>
Reviewed-by: Mike Rapoport <[email protected]>
Reviewed-by: Vincenzo Frascino <[email protected]>
Reviewed-by: Catalin Marinas <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Eric Auger <[email protected]>
Cc: Felix Kuehling <[email protected]>
Cc: Jens Wiklander <[email protected]>
Cc: Khalid Aziz <[email protected]>
Cc: Mauro Carvalho Chehab <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>